Signaling system



J. J. GILBERT Il IVY ALIA VVV 5E Il l AM vnr HVV AAA

SIGNALING SYSTEM Filed Jan. 27, 1932 July l1, 1933.

/A/l/EA/TOR J J G/L BERT ATTORNEY Patented July 11, 1933 UNITED STATESPATENT oFF-icE JOHN J. GILBERT, or noUGLes'roN, NEW Your; essierNonl ToBELL TELEEHONE LABO- RATORIES, INooRPo-Rernn, or* NEW YORK, N; Y., ACORPORATION oF NEWYORK Application med aanname?, i932.' serial No.589,195.

This invention relates to the transmission of electric currents, andprovides improvements in the tivo-Way transmission ofsuch currents, forinstance, in the two-Way repeating of telephone or carrier telegraphcurrents.

It has been discovered that Where useis made of high speed switchingmeans, or other quick-operating meansresponsive to transmission, forcontrolling a repeating circuit, in order that When the repeatingcircuitisin use it may operate effectively in only one direction at a time, theoperation of thev control means may be deleteriously adected bytransient. energyrwhich may discharge from the line connected to theoutput of the repeater` after the input to that line has ceased. Ingeneral, when the input transmission to the line ceases, some energywill return from it and Will enter the output ofthe repeater. lThere arevarious factors Vwhich may cause energy sent out by a repeater toreenter it. For example, the energy may be reliected from terminalapparatus or it may be stored in the line and sent back to therepeater,or stored in terminal apparatus and fed back to the line and repeaterupon cessation of input from-the repeater to the line.

In addition to the kick-back energy which manifests itself in the formof an alternating current, a residual charge remains upon the line afterthe transmitter has been disconnected from the line. This residualcharge produces a slowly decaying current in any direct current pathwhich is present at the terminal. In the case of a long submarine cablethe initial value of this current is about 30 to 40 decibels down fromthe level of the previously impressed signals; it may take several timesthe transmission time of the cable for this current to decay to a value100 db. further down; rIhis decaying or relaxation current is duechiefly to the low frequency components of the transmitted signals whichare much slowerin dying out than`V is that when the receiving amplifieris connected to the line when such a current is Howing, there is asudden change in terminal impedance which generates high frequencyvoltages; currents produced by these Voltages are transmitted throughthe receiving amplifier' as a disturbing click.

A general` object of this invention is to avoid the effect uponreceiving apparatus connected to a line conductor of the residual chargeWhich remains stored in the conductor after the transmitter has beendisconnected.

In order to attain the above and other objects of this invention, thereceiving or output circuit ofthe cable or transmission line is bridgedbetweenV conjugate points of the transmission line and an artificialline, and the transmitter is connected to the apex of the bridgecircuit. The side branch of the bridge circuit Which is connected to theartificial line includes means such as a lter or choke coil whereby theamplitudes of high frequency currents transmittedinto the artificialline are small compared With those Vcurrents transmitted into thecable,so that the low frequency components of the transmitted currents aretransmitted in equal proportions into the cable and the artificial line.After the transmitter has been disconnected,there are residual'V charges(relaxation currents, chiefly of low frequency components) in both thetransmission line and the artificial line. These charges from the twolines balance each other and consequently produce no resultantefect uponthe receiving circuit.

In general, high frequency components of telephone signals die outrapidly, and inthe normal operation of a system such as is contemplatedby this invention, these high frequency currents are practicallycompletely dissipated before the receiving circuit is connected to theline. It is usually important that high frequencies be impressed uponthe transmission line in full volume. Therefore, a feature of thisinvention is a filter or choke coil arrangement for preventing theartificial line from exerting a drain on the high frequency componentsfrom the transmitter. By virtue of this feature, although the loW"frequency components sent to thel transmission Vline and the artificialline are y approximately equal, the high frequency components Whichenter the artificial line are very small.

The invention may be better understood from the following detaileddescription of its features and of its principles of operation, inconnection With vthe accompanying drawing in Which identical referencecharacters designate similar parts, and in which:

Fig. I shows aj diagrammatic representation of a submarine telephonesystem constituting one embodiment of the invention; and

Fig. 2 shows a diagrammatic representation of a submarine telephonesystem consti'- tuting another embodiment of the invention; In F ig. lthe outputs of a transmitter TV capacity type as shown. The bridgecircuit also contains the armature contacts of two voice operated relaysl0 and l1, one in eachy branch. These lrelays are controlled by thetransmitter T and the amplifying detector AD to automatically closetheir contacts on transmission of signals and to open them ou receptionofsignals. The receiving or output circuit R of the system is bridged',

shown, between conjugate points ofthe cable C and' the artificial lineAL. The receiving circuit includes the armature Contact of a. voiceoperated relay l2. Relay l2 Works` in a manner opposite to that of voiceoperated relays 10 and l1, that is, it is open on transmission andclosed on reception of sig'- nals.. The relays l0, 11 and l2 are of thefast-operating and slow-releasing type. The resistances R and R areadjusted so that the low frequencies transmitted into the cable and theartificial line are equal in The filter L is chosen so as to havenegligible i impedance compared with that of resistance R at lowfrequencies, but highimpedance compared With that of R at highxfrequencies, so that thev am-plitudes of the high frequency currentstransmitted into the artificial line AL Will. be small compared Withthose of the current transmitted into the cable. This arrangementpossesses the further advantage that the load on the transmitter isreduced..

The operation of the system shown in Fig. l is as follows: Ve assume thearmatures of relays l0, ll and l2 in the position shown which is thatcorrespondingF to the transmission of speech from the transmitter T. Asstated above, theseV relays release their'respective armatures with adelayed action. When amplitude.A

the near end subscriber stops talking, the contacts of relays l0 vand llremain closed for a short time interval to allow the Weak endings of thesignal currents to pass, even though they fail to maintain the output ofthe amplifying-detector AD" operative. After that time has elapsed thevcontacts of relays 10 and l1 are released (opened) whereby thetransmitter is disconnected from the line. At'this moment there areresidual charges of equal potentials, com posed chiefly of low frequencycurrents, i. e., the relaxation currents, in the transmission liney Cand the artificial line AL. The armature contact of relay l2 is nowclosed and thusl the charges in the twolines being of equal" potentials,balance eachother, andcon-4' turbance) in the receiving circuit.

vIn the 'mod`ficationof the invention Which is. shown in Fig. 2, thesubmarine telephone system illustrated' comprises a main cable Cl andtransmitting and receiving earth cables TEC and REC, respectively. Thereceiving earth' cable REC is connected"n tothe primary Winding of thereceiving transformer RT and the main cable CI is connec-ted;V toV theprimary Pfof receiving transformer RT.Q' The conta-ct ofvoice operatedrelay l0l is closed on transmission and open on reception` of signals.The secondary Winding S- of the transmitting transformer TT is connectedas shown over theA armature of relay 10; to the main cable Cl and to thetransmitting earth` cable TEC'. A filter Ll isconnected in series: withthe artificialv line ALl simulating thefcable. In a manner similar tofilter L of Fig. l, the filter Ll is' constructed so a-sto offer a lowimpedance tov loW frequencies and a high impedance to high frequencies,in order to prevent unnecessary drain onfthe'transmitting amplifier. Inorder to prevent unbalancing' the vnetwork on reception-v of signals,and' to cause, statics or interfering voltages in the receiving earthcable REC to balancey Statics or interfering voltages in the main cableC1, a similar lilter L2 and artificial AL2 line are Vconnected as showninV the circuit of the' receiving earth cab-le REC. The-terminalsections' of thel sending and receiving earth connections TEG and RECrespectively and of the main cable C1 may be enclosed Yin the same armor(as shown) to formv a Ycomposite cable C. At a; short distance (le. gabout 5 miles) from shore, the conductor ofthe sending earth cable TECis connected to the armorv of casequently"` produce noappreciable effect(disble: C,fan.dat a distance ofthe order of about` 200r miles fromshore the. conductor of the receiving earthl cable REG is connected asshown through an impedanceY element Z to the4 grounded concentric returnconductor; CR of the mainy the distantendt. The provision: of the cable-Cl which extends.: to;V

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pedance element Z is for the purpose of terminating the receiving earthREC in such a manner that its impedance, as Vseen from the nearterminal, closely approximates that of the main cable C1. f

The operation of the embodiment of the invention shown in Fig. 2 is asfollows: We assume the armatures of relays 10 and 12 in the positionshown which is that corresponding to the transmission of speech by thetransmitter T. Relays 10 and 12 release their armatures slowly. Duringspeech transmission the primary windingP of the receiving transformerR-T is short-circuited so as to prevent any of the transmitted energyfrom Aaffecting the receiver R and to permit the transmitted energy todivide between the transmission line (conductor C1) and the artificialline AL1 in the proper manner. When the near end subscriber stopsspeaking, the armature of relay 12 is released first, and the releaselof the armature of relay 12 removes the short-circuit across primarywinding I). Relay 10,'in Vreleasing its armature, disconnects thetransmitter T from the line. The residual charges stored in the cableand in the artificial line, which are of approximately equal values,balance each other and have no serious disturbing ef-v fect upon thereceiver R.

Vhat is claimed is:

V1. A submarine signaling system comprising a cable, a receivingcircuit, means for `connecting and disconnecting said cable to `and fromthe circuit at frequent intervals, andv means including an articial linefor overcoming the effects of residual cable voltages in said circuit atthe instant when said cable is connected thereto. Y

2. In a signaling system, a transmission line, a sending mechanism and areceiving mechanism, means for alternately connectingand disconnectingsaid mechanism to and from said'line, and means for preventing excessivecurrents at the time of connecting the receivingV mechanism to thetransmission line, said means comprising a device connectable to thereceiving mechanism and adapted to counteract the residual line voltage.Y

3. In a signaling system, a transmission line, an artificial line', areceiving circuit con-V nectable toboth lines, meansfor .transmitting ilow frequency currentsin equal, andv high frequency currents in unequalyproportions,'

into said transmission line and artificial line respectively, wherebyresidualcharges in the transmission line due to previously transmittedlow frequency currents do not in- `juriously affect the receivingcircuit whenV the latter is connected to said line. n

4. System as defined in claim 3 in which said frequency transmittingmeans includes a filter and a resistance element, said ilter having alow impedance at low frequencies and a hi 'h impedance at highfrequency, as compare with the impedance of said resistance element. 7

5. A'signaling system comprising a transmitting circuit and a receivingcircuit', a line f conductor and a balancing conductor therefor, meansfor alternately connecting and disconnecting said line conductor to andfrom said receiving circuit, the receiving circuit being bridged toconjugate points of saidv conductors, whereby, the effect upon thereceiving circuit of any residual charge which remains stored in saidconductors after disconnection therefroiii of the transmitting circuitis reduced. f Y

6. A deep sea telephone system comprising a main cable, a sending earthcable and a receiving earth cable, a transmitting circuit adapted to beconnected to points across said main cable and saidvsending earth cable,a

receiving circuit adapted to be coupled to points between said maincable and said receiving earth cable, means for switching said maincable to and from thereceiving circuit,

'and an artificial or balancing cable for said main cable, whereby lowfrequencycurrents in said main cable are prevented from detrimentallyaffecting said receiving circuit.

7 System as defined in claim 6, further y' characterized by a balancingcable across points of thel sending earth cable and the receiving earthcable respectively whereby the effects of interfering currents in thereceiving sea earth cable are causedto balance the iio effects ofinterfering currents in the main cable.

In witness whereof, I hereuntoV subscribe my name this 21st day ofJanuary, 1932. JOHN J. GILBERT.

